This is a study to evaluate the tolerability and effectiveness of Rofecoxib 25 mg. q.d. vs. Naproxen 500 mg. B.I.D. after 12 weeks of treatment in patient with osteoarthritis of the knee, hip, hand, or spine. Osteoarthritis will be diagnosed with standardized clinical criteria. Patients who regularly use non steroidal anti-inflammatory or acetaminophen for the treatment of osteoarthritis of the study joint will be studied. The primary aim is to test the gastrointestinal tolerability of the investigational drug.